How thick should the AR 400 be for different calibers? Discount Steel in Ft. Worth sells it in smaller pieces online. I have been wanting to build some targets, but was never sure what steel specifically to use.

I want to build some smaller spinner type targets for 22LR, 22 Mag and some larger ones for .308, 30-06 as well as 9mm & .45. I would imagine the thickness required for '06-.308 would be good for all the other caliber rounds although thinner plate for shooting with 22LR would be a lot cheaper. I thought Ammo was high, Jeez!